Structural sandwich plate members are described in U.S. Pat. No. 5,778,813 and U.S. Pat. No. 6,050,208, which documents are hereby incorporated by reference, and comprise outer metal, e.g. steel, plates bonded together with an intermediate elastomer core, e.g. of unfoamed polyurethane. These sandwich plate systems, commercialised under the trade mark SPS, may be used in many forms of construction to replace stiffened steel plates and greatly simplify the resultant structures, improving strength and structural performance (e.g. stiffness, damping characteristics) while saving weight. Further developments of these structural sandwich plate members are described in WO 01/32414, also incorporated hereby by reference. As described therein, foam forms may be incorporated in the core layer to reduce weight and transverse metal sheer plates may be added to improve stiffness.
According to the teachings of WO 01/32414 the foam forms can be either hollow or solid. Hollow forms generate a greater weight reduction and are therefore advantageous. The forms described in that document are not confined to being made of light weight foam material and can also be made of other materials such as wood or steel boxes.
International Patent Application WO 02/078948 is a further development of the concept of including hollow forms and describes forms that are easy to manufacture and assemble, in particular hollow elongate forms made from snap-together pieces are described.
International Patent Application WO 02/20341 describes a method whereby existing structures may be reinforced or reinstated by welding a plate in spaced relation to a panel of the existing structure and injecting uncured plastics or polymer material into the resulting cavity such that, when the injected material cures, it bonds to the existing panel and new plate with sufficient strength to transfer shear forces between them. The resulting structure behaves as a single body. This method is particularly advantageous in that it can usually be performed more quickly than the conventional technique of cutting out the damaged or corroded plates in the existing structure and welding a new plate in place. Also described is a method of reinforcing a pipeline by welding a jacket around the pipeline and filling the space between the pipeline and jacket with plastics or polymer material.
Some off-shore structures are supported by hollow tubular steel columns resting, or driven into, the sea floor. These columns are particularly susceptible to corrosion and are difficult to repair or replace. The techniques described in WO 02/20341 are particularly difficult to apply because of the difficulties of welding and injecting the core material underwater, especially at depth. It would also be difficult to maintain the inner surfaces of the cavity sufficiently clean and dry for the cured core to bond to the metal layers with sufficient strength. However, the advantages of an SPS(™) structure would be particularly beneficial in these types of structures.